Flow-eveners for wood chip digesters



F. B. K. GREEN FLOW-*EVENERS FOR WOOD CHIP DIGESTERS Jan. 28, 1958 3 Sheets-Sheet 1 Filed April 12, 1954 Snventor Frank B. K. Green W mAaew 3% R mm mm Gttorneg Jan. 28, 1958 F, B. K. GREEN 2,821,476

FLOW-EVENEIRS FQR WOOD CHIP DIGESTERS Filed April 12, 1954 A 5 Sheets-Sheet 2 .5? I L 1 I I Q 0 m N s I s i g R cu s S .9 S

m .9" l LL 3n'ventor Frdnk B. K. Green B1; mmwuw (Ittorneg Jan. 28, 1958 F. B. K. GREEN FLOW-'EVENERS FOR WOOD CHIP DIGESTERS 3 Sheets-Sheet 3 Filgd April 12 1954 we; 35w ton o mmon a: :35 25a 3.9.5

uconxm 2 E09. $3 @520 39.22:. 5.65813 23E 969 E tao INVENIQK; Frohk 8. K. Green 'AT'TORNEY United States Patent Ofitice 2,821,476 P tented Jan. 28, 1958 FLOW-EVENERS FUR WOOD CHIP DIGESTERS Frank B. K. Green, Massapequa, N. Y., assignor to Pandia, Inc., New York, N. Y., a corporation of New York Application April 12, 1954, Serial No. 422,377

2 Claims. (Cl. 92-6) This invention relates to the continuous digestion or cooking of ligno-cellulosic material, such as wood chips, to be made into pulp used for formation on a papermaking machine or the like into sheets, such as paper. The invention is an improvement on the continuous diges'tion apparatus disclosed in the U. S. patent to Beveridge and Kehoe-No. 2,422,522, patented June 17, 1947, and also on the improved continuous digestion apparatus shown in the U. S. patent to Kehoe, Surino and Goodwin-No. 2,616,802, dated Nov. 5, 1952. This application is a continuation-in-part of my application Serial No. 261,279, filed December 12, 1951, and now aban- Cloned.

In general, the above patents disclose apparatus wherein continuous digestion is carried out effectively in a closed flow-through tubular path in which is maintained a super-pressure as well as super-boiling temperature and embodied in a plurality of horizontal superposed conduits or pipes in each of which is a driven shaft-bearing screw conveyor with a free-fall vertical neck-like connection between adjacent ends of the superjacent pipe and a subjacent pipe as well as with a similar free-fall feed connection leading into the other end of the superjacent pipe and another such free-fall exit connection from the other end of the subjacent pipe. Means are provided for supplying ligno-cellulosic material to the feed connection, and so are means for removing treated material from the exit connection and conducting it to a refiner or to a device for fragmentizing the treated wood chips. The atmosphere of the flow-path is made up of saturated steam with or without chemicals, such as caustic soda, for rendering water-soluble the ligneous encrustations on the cellulosic fibers. In such apparatus, it has been found that, in general, chips could be supplied to the horizontal pipes in quantity not greater than enough to fill thepipes to be somewhat more than half full, and this upper load limit is determined by the fact that the discharge of chips from any screw conveyor is inherently spasmotic. The slower the speed and the larger the dimeter of the screw, the more of a problem it is to even out the discharge. So an object of this invention is to provide means for evening out the discharge of chips from the end of the screw conveyor in each pipe so that the discharge from that pipe is substantially uniform. In this way the flow-through rate or capacity of 'the pipe is increased without increase in the size and number of the pipes.

It is understandable that the break-away of a large part of the quantity of chips in each screw flight (or between two flights) is not going to occur at the same point in every revolution of the screw conveyor. The discharge from the pipes is massive at one time and is withheld at another time, thus causing the flights in the subjacent pipe to fill unevenly. This unevenness gets progressively worse especially when the apparatus has morethan two superposed horizontal pipes (for some have as many as "eight such pipes). While-it seems remote that this could cause plugging somewhere ahead thereof, it has caused trouble in that it has prevented uniform chip turn-over and thus non-uniform chip treatment.

So it is another object of this invention not only to correct this erratic discharge of chips from the end of a treatment pipe, but to assure uniform and even delivery of chips through the vertical free-fall connection to the intake end of the next subjacent treatment pipe so that the flow-through rate of the latter pipe will be constant.

In order to appreciate the problem to be solved by this invention, some idea should be had of the sizes of the apparatus involved. The horizontal pipes with their screw conveyors through which the wood chips are passed, can be as large as 36 inches in diameter. In some installations there can be eight or even ten of these pipes, so actually these digesters are enormous machines. On the other hand, a normal wood chip is about the size of a half dollar except perhaps a little thicker. A maximum size chip could fairly be said not to substantially exceed a silver dollar in diameter or twice a dollar in thickness. These chips are fed to the digester by the thousands, and as they pass through a horizontal pipe, they are subjected to super-boiling temperature at super-steam pressure with the result that they become saturated and thus softened.

As the progressive screw conveyor is driven, it exerts a very high compressive force on the softened chips, so they are squeezed and compressed to stick together clingingly until they are compacted into plug form. This plug is so compact that as the mass progresses from the exit end of the horizontal pipe over the free-fall connection, instead of the chips falling apart from their plug form, the plug continues .to be expelled sufiiciently until some of it breaks off as chunks to fall down the free-fall connection. Such chunks or hunks of stuck-together chips make the feed to the subjacent pipe erratic and uneven. Indeed, the clinging condition of the compacted chips causes them to arch in the free-fall connection, and this occasionally stops completely all feed to the subjacent pipe. Another condition also exists, namely, the angle of repose of the wood chips before they are treated in the first horizontal pipe is about 45, whereas they are discharged from that pipe, their angle of repose has been immensely increased, indeed, to or even more. This makes for undependable feed of them to the next lower pipe, so the assurance of constancy of feed at this point is the major object of this invention. But it is also another object of this invention to break up the plug form of the chips exiting from the horizontal pipe into the free-fall connection by providing means for undercutting the periphery of that plug in a way that leaves the inner portion of the plug in what may be called a boss. The undercutting leaves space in which the boss portion can expand, and in expanding, it tends to disintegrate. Yet another object of this invention is to provide means for facilitating the disintegration of that boss portion.

So, in broad terms, it may be said that an important feature of the invention is the provision, in apparatus of the type above described, of devices which can be depended upon to even out or render substantially constant the flow of chips during their transit along the enclosed flow-path wherein they receive their digestion treatment. And in more specific terms, some of the objects of the invention can be attained by the use of plug-undercutting and disintegrating interrupted edges rotatable with the shaft-bearing screw conveyor while located in the horizontal pipe over the vertical connection through which the chips descend from that screw conveyor. Other ob jects-of the invention can be attained by the formation of the last full flight of the screw conveyor means ad- 3 jacent the plane of the interrupted edges of gradually reduced diameter from the diameter of the remaining flights. Still other objects of the invention can be attained by more particular details of construction of these edges and the means for supporting them as described and defined hereinafter.

As this invention may be embodied in several forms without departing from the spirit or essential characteristics thereof, the present embodiment is therefore illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them, and all changes that fall within the metes and bounds of the claims, or of equivalents of such metes and bounds, are therefore intended to be embraced by those claims.

The preferred form in which I have contemplated applying my invention is clearly illustrated in the accompanying drawings, wherein:

Figure l is a somewhat diagrammatic view with parts broken away and showing a practical embodiment of the invention with its associated apparatus, but with no chips therein. Fig. 2 is an enlarged partial side elevational view of one end of a conduit with parts broken away, showing the details of the screw conveyor at that end and the interrupted edges mounted for rotational movement with the screw conveyor, as well as the associated structure of the fiovwevener apparatus. Fig. 3 is a vertical transverse sectional view taken substantially along the plane of line 33 of Fig. 2. Fig. 4 is a front elevational view of one of the interrupted edge members of the flow-evener. Fig. 5 is a partial isometrical view of the plug of chips that is undercut and disintegrated by the flow-evener. Fig. 6 shows a detail.

Referring more particularly to Figure 1, the apparatus has a feeding-in zone A, a preheating zone B, intermediate zones C and D, and a discharge zone E having in its lower section a zone F of a mobilized suspension of fragmentized chips, slivers and fiber bundles, discharged therefrom through an emission conduit leading to a refiner (not shown).

More specifically, the feeding-in zone A comprises a feed hopper 11 for the wood chips that conducts them to a screw feeder 12, rotatably driven in the tapered necklike casing 13 wherein the screw feeder 12 forms the chips into a compacted plug formation Within the conduit section 14, the plug formation being sufficiently dense to prevent heat and pressure loss from the preheating zone B. Conduit or pipe section is connected to the conduit section 14 and receives the wood chips by means of the forced feed of the screw feeder 12. Saturated steam is supplied to the conduit section 15 through the valved injector pipe 16 for maintaining super-atmospheric pressure and temperature above 212 F. throughout the apparatus to the discharge zone E for softening the middle lamella or lignaccous incrustants of the fibers.

The conduit or pipe section 15 is of substantially greater diameter than the conduit section 14 so that as the chips expand under the influence of the moist heat in the preheating zone, they do not fill the conduit section 15 substantially over the axial line thereof. Screw conveyor means formed as a continuation of the screw feeder 12 or as a separate feeder is provided for the purpose of carefully controlling the rate of progress through the preheating zone in order that there be no localized over-treatment or degradation of the cellulosic fibers.

The preheating zone further includes a T-conduit section 17 which is connected to the conduit section 15 by means of the stem or outlook portion 18. The body portion 19 of the T-conduit section has a valved injection pipe 20 connected to one end thereof for supplying chemical in the event that chemical or semi-chemical pulp rather than merely heat-treated pulp is desired. The chemical used is such as to be reactive with the ligneous incrustants on the cellulosic fibers of the chips to render the normally '4 water-insoluble incrustants while in situ to be watersoluble.

The body 19 of the T-conduit section acts as a down pipe through which the chips may freely fall for entry into the free-fall feed connection 22 of one :of a plurality of superposed material supporting conduits or pipes of the intermediate zones C and D. It is to be understood that there may be as many as eight or more superposed conduits or pipes and that the number shown is by way of example and for clarity. In each of the superposed conduits or pipes 24 and 26 is a driven shaft-bearing screw conveyor 28 and 30 respectively for effecting movement of the ligno-cellulosic material being treated through the conduits or pipes 24 and 26. A free-fall vertical neck-like connection 32 between adjacent ends of the superjacent pipe 24 and the subjacent pipe 26, and remote from the feed connection of the superjacent pipe, provides for communication between the pipes whereby the material passes in series through the plurality of superposed pipes. The lowermost pipe 26 has a free-fall exit connection 34 at the end remote from the neck-like connection 32 for conducting the material to a refiner or to a device for fragmentizing the treated wood chips in the discharge zone E.

The means for fragmentizing the wood chips includes a down-pipe 36 connected with the free-fall connection 34 by means of the conduit section 38. The down-pipe 36 merges into an impeller compartment 40 closed off at its bottom by closure wall or bottom 42 through which extends a motor-driven shaft 44. The shaft 44 has an impeller 46 with a plurality of blades 48 at the upper end thereof within the impeller compartment 40. In the horizontal plane of the impeller, there is at least one discharge outlet orifice or port 50 opening into a discharge conduit 58 that leads the pulp to further treatment. The clfective size of the discharge orifice 50 is controlled by manipulation of the handles or levers 54 and 56. The steam-softened and fragmentized material passes from the discharge conduit 52 to the conduit 58 which conducts the material to a further treatment or refining station G. Inasmuch as the present invention concerns itself primarily with the means for evening out the discharge of chips from the end of the screw conveyor in each pipe, a more detailed description of the apparatus with which the present invention is associated is deemed unnecessary.

As seen in Figure l and in greater detail in Figures 2 and 3, the shafts 58 and 60 of the screw conveyors 28 and 30 have fixedly secured to opposing ends thereof, within the conduits or pipes 24 and 26, baffles 62 and 64, which may or may not be used but if used are so located relative to the feed connection 22, free-fall connection 32 and exit connection, as to confine the flow of material through the series of conduits and connections. Each of the bafiles is of truncated conical form with the conical surface thereof making about a 20 angle with the base of the cone. The shafts also have fixedly secured thereto a flow-evener having a plurality of flat, relatively thin radial arms 66. One of the arms is shown enlarged in Figure 4. The arms 66 have parallel leading and trailing edges 68 and 70, respectively, defining plug-engaging planes disposed in angular relation to the axis of the screw conveyor shafts. The angular relationship with the planes of the arms is such as to break or crumble or tear the plug end engaged by them, but it has been found that 45 angles with the axis of their respective shaft, as best seen in Figure 2, are quite satisfactory.

Each arm 66 has at its outer end a finger 72 which extends therefrom rearwardly of the associated pipe from the adjacent free-fall connection 32 or 34. As best seen in Fig. 2, the fingers 72 are of vane shape and extend at such angles to the axis of the screw shaft, shown as approximately 45 that each finger forms in effect a fragment of a screw flight of markedly greater pitch than the flights of the conveyor screws 28 and 30. These fingers are of suflicient length to extend from their associated arms 66 to positions inwardly of the pipe from the free-fall connections.

Each of the fingers 66 has an inner straight edge 74 in perpendicular relation to the leading edge of its respective arm, and an outer edge 76 extending from the trailing edge of its respective arm and in spaced relation to the inner straight edge, the radius of curvature of the outer arcuate edge 76 being such that when viewed as in Figure 3, the plurality of arcuate edges define substantially a circle 78 concentric with and closely adjacent to the inside surface fitl of each conduit. The finger 72 joins its arm 66 to provide a sharp heel 79. Preferably eight equally spaced arms or eveners are mounted on each shaft adjacent the exit end of the conveyor, the overall diameter of the assembly of arms on the shaft being substantially equal to the diameter of the major portion of the screw conveyor in each conduit.

The leading ends of the inner and outer edges 74 and 76 of each finger define an edge 82 formed at an angle with the leading and trailing edges 68 and 70 of the arms. It will thus be seen that the arms and fingers constitute members, and the group of members provides interrupted undercutting edges 82 which are adapted to engage successively the plugged chips being conveyed through the conduit. These fingers undercut at U the plug form taken by the compacted chips, as shown in Figure 5, whereby on the plug P, as it rotates with the screw flight, there is left a boss portion B which in turn is progressively broken or crumbled off, until the plug is disintegrated back into chips loosened from each other and cut or pulled apart,

so that they fall down the free-fall connection 32 as discrete fragments.

The screw conveyor of each conduit is of substantially uniform diameter with the exception of the terminal flight adjacent the flow-evener, as at 84 in Figure 2, wherein the diameter of the last flight gradually decreases from normal diameter to slightly greater than one-half its normal diameter. The decrease in diameter occurs in a little over 90 of the last flight, as seen in Figure 3 at 86. With the arrangement as shown, the feed of chips will be such as to effect an accumulation of chips in plug form immediately in front of the flow-evener, the reduced diameter screw conveyor portion operating to give the plug-undercutting arms space in which to work without engaging the flights of the screw conveyor. The rotating arms and toed-in fingers of the fiow-evener break up the mass of chips passing from the conduit 24, at the same time loosening them from each other and effecting a thorough mixing thereof. The action of the flow-evener is such as to effect continual rearrangement of the chips with respect to each other, resulting in a more uniformly cooked product.

Operation The wood chips W are supplied to the hopper of the feeding-in zone A, and the screw feeder 12 forces the chips into the preheater zone B under conditions that prevent any' substantial loss of steam therefrom. Saturated steam is supplied through the steam injector pipe 16 whereby the system can be maintained at a temperature above 212 F. and at a super-atmospheric pressure. The screw conveyors 28 and 30 in the material supporting pipes or conduits 24 and '26 have as their purpose the determination of the rate of progression of the chips therealong whereby the time of transit of the chips through the digester is under the control of the operator. Although only two conduits 24 and 26 are illustrated as comprising the intermediate sections, more than two conduits can be used, and, indeed, digesters have been designed that make use of as many as eight or more superposed materialsupporting conduit having suitable connections therebetween.

The discharge zone E of the digester finds embodiment in a vertical pipe down which chip-forms freely fall from the screw conveyor means 30. In so falling the chips on counter in zone F what may be termed a cushion of a mobilized, fluidized'suspension of chips, chip-fragments, shives and fiber-bundles. This suspension-thatis generally annular in shape is produced by intense agitation and turbulence, generated in the zone by means such'as the impeller 46 and its blades 48. High speed rotation of the impeller causes the chip-forms to be broken along their lines of cleavage into fragments or shives, and those fragments in turn are further broken down into fiber-bundles or slivers, but all without cutting. This is accomplished by the speed of the blades which agita'te'the chips and direct the same against the walls engaging the impeller and the annular shoulder.

The suspension is impelled out through orifices 50 partly due to the stream of steam flowing therethrough, and partly due to the impulses imparted thereto by the .impeller. The diameter of this orifice is important in that it operates to fragmentize the material further along its lines of cleavage and to limit the maximum diameter of the fragments thereof which can be emitted through that orifice. To aid in the control of the maximum particle size in the emitted suspension, the diameter of the screening orifice desired is under the control of the operator by means of the handle or lever 56.

From the orifice, the discharged suspension is conducted through the emission conduit 58 of increasing crosssection area to be emitted to the atmosphere. This expanding emission conduit brings about a gradually decreasing pressure on the suspension so that when the fibrous material thereof does reach the atmosphere, no force is exerted on them which tends to explode or otherwise degrade these fibers.

Operation of the improvement It is to be noted that in previous systems, theoretically speaking, with each full rotation of the screw conveyor, the wood chips progress the length of one full flight with a charge of chips equal in length to one full flight, freely falling through the connection to the next conduit. Under practical conditions, however, the wood chips are unevenly fed by one conveyor to the next, and as the movement continues through several superposed conduits, the unevenness becomes progressively worse.

in the present arrangement, the plug P of chips encounters the teed-in fingers '72 which undercut the plug peripherally at U, leaving extending from the plug a boss-like portion B. The toed-in fingers thus make a peripheral undercut in the end of the plug, giving the boss space in which to expand and to disintegrate outwardly. If the boss could not expand outwardly, there would be a tendency to plug even withthe arms'66. But the arms 66, angled as they are to present cutting leading edges 68, progressively cut into the boss B, and thus disintegrate it into discrete particles or fragments of chips, or at least it tends to pull the chips apart from their clinging compaction into plug form. The decreased diameter portion 84 of the screw conveyors allows space in which the undercutting of the plug by the toed-in fingers 72 can take place. The arms, with their toed-in fingers are arranged to move at a peripheral speed greater than the rate of forward progress of the plugged mass through the horizontal pipe. Upon each complete rotation of the screw conveyor, a charge of discrete Wood chips disintegrated from their plugged form, closely approximating the theoretical optimum, is progressed for passage through the connection 32. The progression of the plugged charge is accelerated in the outer portion of the mass by the plurality of finger members, thus assuring rearrangement and repositioning of the chips as well as pulling apart any two or more chips that may be sticking together, so that notonly are the chips loosened from each other, broken up, turned over and thoroughly mixed, but the feed to the subjacent conduit has been effectively rendered substantially even.

Without the fiow-evener arms, the chips tend to hang together and stay in the screw until they assume a greater angle than the angle of repose. When this occurs, a mass of chips is apt to slide away from the screw flight and into the vertical pipe. As the flow-evener arms move the chips forward faster than the screw itself, because of their action as parts of screw flights of greater pitch than the screw, even though the chips are sufficiently compacted to hang together, the undercutting of the evener arms at the greatest diameter of the pipe allows the compacted mass of chips to break up and flow evenly into the vertical pipe. Without anything underneath the mass of chips remaining in the screw, gravity overcomes the tendency of the chips to stick together and they are discharged as individual chips rather than as a mass. As the flow-evener arms come down from the side of the pipe toward the bottom, the tendency of the chips is to fall down because of the arms cutting out underneath the compacted mass, and as the arms reach the bottom the effect is maximum.

So the eveners to even out the flow of chips are very important because they not only improve operating conditions all through the conduit, but they tend to prevent plugging or arching in the conduit or in the fragmentizing discharge mechanism, since the normal low angle of the chips is restored. There is also a substantial reduction in the power used to operate the bladed impeller in that mechanism as well as in the quantity of steam used to discharge the stock. Without the flow-eveners, there is an intermittent load on the discharge mechanism because of the uneven discharge of chips into the discharge mechanism, so that the power consumption constantly fluctuates and the equipment has to be of suflicient size to take care of the maximum load, which results in operating inefliciency when partial loading occursand partial loading occurs most of the time. When the flow of chips is even, the load is even and the maximum load is reduced. Without the flow-eveners, the size of the orifice has to be regulated for the maximum discharge of stock which means that during the larger part of the time, more steam is being discharged than is actually necessary. But with the flow-eveners, the discharge of stock is uniform; the orifice size can be kept down; and there is thus a saving in the consumption of steam.

From the foregoing description of the system and the means whereby the discharge of chips from the end of the screw conveyor means of each pipe or conduit can be evened out and maintained substantially uniform, it is believed that the objects hereinbefore set forth have been effectively attained.

I claim:

1. In continuous digesting apparatus of the character described including a generally horizontally extending tube having an inlet at one end for receiving cellulosic material for treatment therein and having a downwardly extending outlet at the opposite end thereof, the combination of a screw conveyor in said tube including a shaft extending through the length of said tube and screw fiights on said shaft for advancing said material from said inlet to said outlet while tending to compact said material into a generally plug-like mass adjacent said outlet, said screw flights terminating short of said outlet and being of predetermined pitch causing advance of said mass at a predetermined maximum linear rate, a plurality of arms extending generally radially from said shaft adjacent said outlet and between the outlet end of said tube and the adjacent end of said screw flights, vaneshaped fingers on the outer ends of said arms extending therefrom toward said screw flights adjacent the inner wall of said tube, said vane-shaped fingers being arranged to form fragments of screw flights of greater pitch than said conveyor screw flights and of substantial axial extent with respect to the edges of said arms nearest said conveyor screw flights to cut away the outer peripheral portion of said mass for gravity discharge through said outlet prior to the central portion of said mass by advancing said outer peripheral portion thereof at an increased rate with respect to said central portion and thereby to provide space in said tube surrounding said central portion for expansion thereof prior to reaching said outlet, said arms being formed of relatively thin and flat material and each having the forward edge thereof spaced lengthwise of the axis of said shaft from the leading end of said finger thereon to present a cutting edge, and said arms being arranged substantially uniformly in planes inclined with respect to said shaft axis for cooperation with said cutting edges to effect progressive fragmentation of said expanding central portion of said mass.

2. In continuous digesting apparatus of the character described including a generally horizontally extending tube having an inlet at one end for receiving cellulosic material for treatment therein and having a downwardly extending outlet at the opposite end thereof, the combination of a screw conveyor in said tube including a shaft extending through the length of said tube and screw flights on said shaft for advancing said material from said inlet to said outlet while tending to compact said material into a generally plug-like mass adjacent said outlet, said screw flights terminating short of said outlet and being of predetermined pitch causing advance of said mass at a predetermined maximum linear rate, a plurality of arms extending generally radially from said shaft at a position overlying said outlet and spaced between the center of said outlet and said screw flights, vane-shaped fingers on the outer ends of said arms extending therefrom adjacent the inner wall of said tube toward said screw flights to a position located inwardly of said outlet, said vane-shaped fingers being arranged to form fragments of screw flight of greater pitch than said conveyor screw flights and of substantial axial extent with respect to the edges of said arms nearest said conveyor screw flights to cut away the outer peripheral portion of said mass for accelerated advance to and gravity discharge through said outlet prior to the central portion of said mass by advancing said outer peripheral portion thereof at an increased rate with respect to said central portion and thereby to provide space surrounding said central portion for expansion thereof prior to reaching said arms, said arms being formed of relatively thin and flat material and each having the forward edge thereof extending substantially normally of the axis of said shaft to present a cutting edge, said arms being substantially uniformly arranged in planes inclined with respect to said shaft axis to form additional fragments of screw flights of greater pitch than said conveyor screw flights for cutting away the leading end of said central portion of said mass for gravity discharge through said outlet, each of said fingers having radially spaced inner and outer edges located forwardly of said cutting edge on the associated said arm, and each of said fingers having a leading edge connecting said inner and outer edges thereof and inclined inwardly and rearwardly from said outer edge thereof to said inner edge thereof.

References Cited in the file of this patent UNITED STATES PATENTS 2,292,196 Brynoldt Aug. 4, 1942 2,323,194 Beveridge June 29, 1943 2,663,405 Messing Dec. 22, 1953 FOREIGN PATENTS 82,002 Sweden 1934 U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No 2,821,476

January 28, 1958 Frank B. K. Green It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction and that the said Let ters Patent should read as corrected below.

Column 1, lines 54 and 55 line 27, for "progressive" rea for "dimeter" read --diameter--; column 2,

insert asd --progressing--; line 43, after "Whereas" column 8, line 36, for "flight" read --flights--.

Signed and sealed this 29th day of April 19580 (SEAL) Atteet:

KARL H0 AXLINE ROBERT C. WATSON Atteeting Officer Conmissioner of Patents 

1. IN CONTINUOUS DIGESTING APPARATUS OF THE CHARACTER DESCRIBED INCLUDING A GENERALLY HORIZONTALLY EXTENDING TUBE HAVING AN INLET AT ONE END FOR RECEIVING CELLULOSIC MATERIAL FOR TREATMENT THEREIN AND HAVING A DOWNWARDLY EXTENDING OUTLET AT THE OPPOSITE END THEREOF, THE COMBINATION OF A SCREW CONVEYOR IN SAID TUBE INCLUDING A SHAFT EXTENDING THROUGH THE LENGTH OF SAID TUBE AND SCREW FLIGHTS ON SAID SHAFT FOR ADVANCING SAID MATERIAL FROM SAID INLET TO SAID OUTLET-WHILE TENDING TO COMPACT SAID MATERIAL INTO A GENERALLY PLUG-LIKE MASS ADJCENT SAID OUTLET, SAID SCREW FLIGHTS TERMINATING SHORT OF SAID OUTLET AND BEING OF PREDETERMINED PITCH CAUSING ADVANCE OF SAID MASS AT A PREDETERMINED MAXIMUM LINEAR RATE, A PLURALITY OF ARMS EXTENDING GENERALLY RADIALLY FROM SAID SHAFT ADJACENT SAID OUTLET AND BETWEEN THE OUTLET END OF SAID TUBE AND THE ADJACENT END OF SAID SCREW FLIGHTS, VANESHAPED FINGERS ON THE OUTER ENDS OF SAID ARMS EXTENDING THEREFROM TOWARD SAID SCREW FLIGHTS ADJACENT THE INNER WALL OF SAID TUNE, SAID VANE-SHAPED FINGERS BEING ARRANGED TO FORM FRAGMENTS OF SCREW FLIGHTS OF GREATER PITCH THAN SAID CONEYOR SCREW FLIGHTS AND OF SUBSTANTIAL AXIAL EXTENT WITH RESPECT TO THE EDGES OF SAID ARMS NEAREST SAID CONVEYOR SCREW FLIGHTS TO CUT AWAY THE OUTER PERIPHERAL PORTION OF SAID MASS FOR GRAVITY DISCHARGE THROUGH SAID OUTLET PRIOR TO THE CENTRAL PORTIONOF SAID MASS BY ADVANCING SAID OUTER PERIPHERAL PORTION THEREOF AT AN INCREASED RATE WITH RESPECT TO SAID CENTRAL PORTION AND THEREBY TO PROVIDE SPACE IN SAID TUBE SURRUOUNDING SAID CENTRAL PORTION FOR EXPANSION THEREOF PRIOR TO REACHING SAID OUTLET, AID ARMS BEING FORMED OF RELATIVELY THIN AND FLAT MATERIAL AND EACH HAVING THE FORWARD EDGE THEREOF SPACED LENGTHWISE OF THE AXIS OF SAID SHAFT FROM THE LEADING END OF SAID FINGER THEREON TO PRESENT A CUTTING EDGE, AND SAID ARMS BEING ARRANGED SUBSTANTIALLY UNIFORMLY IN PLANES INCLINED WITH RESPECT TO SAID SHAFT AXIS FOR COOPERATION WITH SAID CUTTING EDGES TO EFFECT PROGRESSIVE FRAGMENTATION OF SAID EXPANDING CENTRAL PORTION OF SAID MASS. 